Thermal fatigue cycling of Be/Cu joining mock-ups

To evaluate beryllium-to-copper joining techniques for potential use by US manufacturers in making first wall components for International Thermonuclear Experimental Reactor (ITER), we tested two mock-ups with S65C beryllium (Be) tiles Hot Isostatic Pressing (HIP) bonded to CuCrZr heat sinks. Under the aegis of the US ITER Project Office, Sandia prepared the mock-ups working with industrial vendors and performed high heat flux testing at Sandiaʹs Plasma Material Test Facility (PMTF) to ascertain the robustness of the Be/Cu joints to 1000 thermal fatigue cycles at a heat flux level of 1.5 MW/m2. Thermal stress analysis provided insight into choosing the heat flux and flow conditions required for accelerated fatigue testing at 1000 cycles and 1.5 MW/m2 that is comparable to the 12,000 cycles and 0.875 MW/m2 required for the ITER First Wall Qualification Mock-ups. ock-up had three Be tiles, 35.5 mm square and 10 mm thick, bonded to a CuCrZr heat sink 134.5 mm × 36 mm × 25 mm with a single bored 12.7 mm (dia.) cooling channel. The bonding techniques included various interlayer metallizations and HIPping at 100 MPa pressure and temperature of 580 or 560 °C for 2 h. Each tile had a thermocouple (TC) in the center 1 mm below the Be/Cu interface. The test arrangement allowed for both mock-ups to be tested at the same time with alternate heating and cooling cycles of equal duration of 30 s. A total power of 12.7 kW was absorbed by the heated area of 4000 mm2 during the on-cycle. The mock-up was cooled by water at 2.3 m/s (0.27 kg/s), 1 MPa and 20 °C inlet temperature. These operating conditions did not permit the mock-ups to cool down to their initial temperature state during the off-cycle. ock-ups survived 1000 cycles with no significant changes. The temperature of the top surface on each reached 254 °C; while the center TCs reached 136 and 139 °C, respectively. Despite localized changes observed in the surface emissivity, the corrected temperature distributions on the surfaces varied by only a few degrees and did not change significantly during testing. We characterized the Be/Cu joint by ultrasonic testing before and after testing and sectioned the mock-ups for further evaluation. This article discusses the fabrication techniques, the results of the ultrasonic and thermal testing, and the time-dependent performance insights from computational fluid dynamics.